Process of packaging semiconductor chip in synthetic resin produced from pressurized granular synthetic resin and molding die used therein

ABSTRACT

A semiconductor chip mounted on a lead frame is sealed in a synthetic resin package through a molding process, and pressure is applied to synthetic resin softened from granular synthetic resin so as to evacuate the air from the synthetic resin before injecting the synthetic resin into cavities formed in a molding die, thereby preventing the synthetic resin package from void.

FIELD OF THE INVENTION

[0001] This invention relates to a semiconductor fabrication technologyand, more particularly, to a process of packaging a semiconductor chipin synthetic resin and a molding die used therein.

DESCRIPTION OF THE RELATED ART

[0002] Conventionally, when an integrated circuit is fabricated on smallareas on a semiconductor wafer, the semiconductor wafer is separatedinto bare chips, and the bare chip is mounted on a lead frame. The leadframe is placed in a cavity of a mold, and synthetic resin is injectedinto the cavity so as to seal the bare chip on the lead frame in thesynthetic resin.

[0003] If granular synthetic resin is used for the packaging, theprocess traces the sequence shown in FIGS. 1A to 1E. Firstly, the priorart molding apparatus is described hereinbelow.

[0004] The prior art molding apparatus largely comprises a molding die 1and an injection unit 2. The molding die 1 is split into an upper half 3and a lower half 4, and cavities 5 and 6 are formed in the upper half 3and the lower half 4, respectively. A pot 7 is inserted into the lowerhalf 4, and is connected through runners 8 to the cavity 6. Ejector pins9 are slidably inserted into holes formed in the lower half 4, and knockout plates 10 are attached to the ejector pins 9.

[0005] On the other hand, the injection unit 2 has an injection cylinder11 fixed to an injection base plate 12 and a plunger 13 movable withrespect to the cylinder 12. Namely, the plunger 13 has one end portionslidably inserted into the cylinder 11 and the other end portionslidably inserted into the pot 7. Though not shown in the drawings, ahydro-pressurizing system is connected to the cylinder 11, and suppliespressurized oil to the cylinder 11 so as to reciprocally move theplunger 13. Knock out rods 14 are upright from the injection base plate12, and the injection base plate 12 is movable toward the lower half 4.

[0006] The prior art packaging process starts with separation of themolding die 1. The lower half 4 is spaced from the upper half 3.Semiconductor bare chips SC are mounted on a lead frame LF, and the leadframe LF is placed on the lower half 4. Although the pressurized oilmaintains the plunger 13 at the upper limit, the injection cylinder 11and the injection base plate 12 stay at a lower limit or a loadingposition, and the plunger 13 defines a space in the pot 7. Granularsynthetic resin SR is inserted into the pot 7 as shown in FIG. 1A, andthe loading work for the granular synthetic resin SR is indicated bypoint a in FIG. 2.

[0007] Subsequently, the lower half 4 starts toward a closed position atpoint b (se FIG. 2), and is brought into contact with the upper half 3at point c (see FIG. 2). Thus, the molding die 1 is closed, and thesemiconductor bare chips SC are accommodated in the cavities 5 as shownin FIG. 1B.

[0008] The granular synthetic resin SR is heated in the pot 7, and ismelted. Thereafter, the cylinder 11 and the injection base plate 12start toward an injecting position at point f (see FIG. 2), and theplunger 13 is also lifted without change the relative position. Thecylinder 11 and the injection base plate 12 reach the injecting positionat point g (see FIG. 2), and the plunger 13 evacuates the molten resinfrom the pot 7 through runners 8 into the cavities 5/6. Thus, the moltenresin is injected from point f to point g, and fills the cavities 5/6.

[0009] The molding die 1 is cooled, and the molten resin is solidifieduntil point h (see FIG. 2), and the semiconductor bare chips SC aresealed in a synthetic resin package as shown in FIG. 1C.

[0010] Subsequently, the lower half starts toward the open position atpoint d (see FIG. 2), and reaches the open position at point e (see FIG.2). The injection cylinder 11 and the plunger 13 starts from theinjecting position and the upper limit at point h (see FIG. 2). Theinjection cylinder 11 and the injection base plate 12 stop at anintermediate position at point 1 (see FIG. 2). However, the plunger 13reaches the lower limit. As a result, the plunger 13 is spaced from thesynthetic resin package PKG at point j as shown in FIG. 1D.

[0011] The injection base 12 starts toward the injecting positiontogether with the injection cylinder 11, and the knock out rods 14 arebrought into contact with the knock out plates 10 on the way toward theinjecting position. The plunger 13 is lifted together with the injectioncylinder 11, and the plunger 13 is brought into contact with thesynthetic resin package PKG also on the way toward the injectingposition as shown in FIG. 1E. The injection base plate 12, the injectioncylinder 11 and the plunger 13 are further moved upwardly by 1·2millimeters, and separate the synthetic resin package PKG from the lowerhalf 4 at point k (see FIG. 2). Thus, the synthetic resin package PKG isseparated from the lower half 4, and is taken out from the molding die1. If the plunger 13 is maintained at the upper limit, the plunger 13 isbrought into contact with the synthetic resin package PKG earlier thanthe ejector pins 9, and the plunger would break the synthetic resinduring the upward motion of the injection base plate 12.

[0012] The injection base plate 12 and the injection cylinder 11 aremoved to the loading position, and the plunger 13 is moved to the upperlimit. Then, the injection apparatus returns to the initial state atpoint m (see FIG. 2).

[0013] The granular synthetic resin SP is easily loaded into the pot 7rather than synthetic resin tablets, and the manufacturer exactlyregulates the amount of synthetic resin to be required. However, thegranular synthetic resin SR carries the air into the pot 7, and void isliable to take place in the synthetic resin package PKG due to the air.The defective products due to the void is ten times larger than thoseproduced from the synthetic resin tablets.

[0014] Japanese Patent Publication of Unexamined Application No.4-164337 proposes to form the granular synthetic resin into syntheticresin tablets before the supply to the molding die. In detail, granularsynthetic resin is supplied to a cylinder, and is heated and pressed inthe cylinder. The molten synthetic resin is shaped into tablets, and thetablet is supplied into the pot of a molding die. While the granularsynthetic resin is being heated and pressed, the air is eliminated fromtherefrom, and the molded synthetic resin is prevented from void.

[0015] However, the granular synthetic resin is firstly changed to thesynthetic resin tablets, and the synthetic resin tablets are used forthe molding. Thus, the prior art packaging process is complicated. Thisis the first problem inherent in the prior art packaging process.

[0016] Another problem of the prior art molding, process disclosed inthe Japanese Patent Publication of Unexamined Application is thecomplicated molding apparatus. The granular synthetic resin is firstlychanged to the synthetic resin tablets, and, thereafter, the syntheticresin tablets are used for the molding. In order to change the granularsynthetic resin to the synthetic resin tablets, the molding apparatusrequires the forming cylinder and the preheating unit for the changefrom the granular synthetic resin to the synthetic resin tablets.Moreover, various kinds of semiconductor device requires the syntheticresin tablets different in size, and the synthetic resin tabletsdifferent in size require different forming cylinders. Therefore, theforming cylinder is chanced depending upon the semiconductor device tobe molded, and the exchanging work consumes a large amount of time andlabor. Thus, the second problem is the requirement of the complicatedmolding apparatus.

SUMMARY OF THE INVENTION

[0017] It is therefore an important object of the present invention toprovide a process for packaging a semiconductor chip in synthetic resinwhich is simple without a complicated molding apparatus.

[0018] To accomplish the object, the present invention proposes toevacuate the air from soft synthetic resin by applying pressure thereto.

[0019] In accordance with one aspect of the present invention, there isprovided a process for packaging a product in synthetic resin,comprising the steps of: a) accommodating a product and granularsynthetic resin in a molding die; b) softening the granular syntheticresin so as to produce soft synthetic resin; c) applying pressure to thesoft synthetic resin so as to evacuate the air therefrom; and d)spreading the soft synthetic resin over an inside space of the moldingdie so as to seal the product in a synthetic resin package.

[0020] In accordance with another aspect of the present invention, thereis provided a molding apparatus comprising a molding die formed withcavities for accommodating a product and runners connected to thecavities, a pot connected to the runners and accommodating granularsynthetic resin, a heating means associated with the pot for heating thegranular synthetic resin so as to produce soft granular synthetic resin,a pressurizing means associated with the pot and applying pressure tothe soft synthetic resin so as to evacuate the air therefrom, and aninjecting means associated with the pot and injecting the soft syntheticresin through the runners into the cavities after the evacuation of theair.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The features and advantages of the process and the molding diewill be more clearly understood from the following description taken inconjunction with the accompanying drawings in which:

[0022]FIGS. 1A to 1E are cross sectional views showing the prior artpackaging process;

[0023]FIG. 2 is a timing chart showing the prior art packaging process;

[0024]FIG. 3 is a cross sectional view showing a molding apparatusaccording to the present invention;

[0025]FIGS. 4A to 4E are cross sectional views slowing a process ofpackaging a semiconductor chip in synthetic resin according to thepresent invention;

[0026]FIG. 5 is a timing chart showing the process for packaging asemiconductor chip in synthetic resin;

[0027]FIG. 6 is a timing chart showing another process for packaging asemiconductor chip in synthetic resin according to the presentinvention;

[0028]FIG. 7 is a timing chart showing yet another process for packaginga semiconductor chip in synthetic resin according to the presentinvention; and

[0029]FIGS. 8A and 8B are cross sectional views showing, essential stepsof still another process for packaging a semiconductor chip in syntheticresin.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

[0030]FIG. 3 illustrates a molding apparatus used in a packaging processembodying the present invention. The molding apparatus largely comprisesa molding die 21 and an injection mechanism 22. The molding die 21 issplit into an upper half 23 and a lower half 24, and cavities 25 and 26are formed in the upper half 23 and the lower half 24, respectively. Apot 27 is inserted into the lower half 24, and is connected throughrunners 28 to the cavity 26. A heater HE is provided in the pot 27, andis connected to an electric power source PW.

[0031] Ejector pins 29 are slidably inserted into holes formed in thelower half 4, and are projectable into the cavity 26. Know out plates 30are attached to the ejector pins 29, a driving mechanism 31 is attachedto the lower half 24 for moving the lower half 24 as indicated by arrowAR1. When the lower half 24 is spaced from the upper half 23, themolding die 21 is in an open position. On the other hand, when the lowerhalf 24 is held in contact with the upper half 23, the molding die 21 isin a closed position.

[0032] On the other hand, the injection mechanism 22 has an injectioncylinder 32 fixed to a base plate 33, and a plunger 34 projects from thecylinder 32. The plunger 34 has one end portion slidably inserted intothe cylinder 32 and the other end portion slidably inserted into the pot27. The cylinder 32 and the plunger 34 define two pressure chambers, anda hydro-pressurizing system 35 is connected to the two pressure chambersin the cylinder 32. The hydro-pressurizing system 35 includes a pump 36and a reservoir tank 37, and a change-over valve 38 selectively connectsthe pump 36 and the reservoir tank 37 to the two chambers throughflexible tubes 39/40. The pump 36 supplies high-pressure oil to one ofthe pressure chambers, and the high pressure oil returns from the otherpressure chamber to the reservoir tank 37. When the high pressure oil issupplied to the lower pressure chamber, the plunger 34 projects from thecylinder 32, and is slidably moved in the pot 27. On the other hand,when the change-over valve 39 supplies the high-pressure oil to theupper pressure chamber, the plunger 34 is retracted into the cylinder32. Thus, the plunger 34 is moved with respect to the cylinder 32, andis changed between an upper limit and a lower limit.

[0033] Knock out rods 41 are upright from the base plate 33, and arealigned with the knock out plates 30. A lifter 42 is connected to thebase plate 33, and moves the base plate 33 and, accordingly, thecylinder 32 in the direction indicated by arrow AR2. Thus, the lifter 42changes the base plate 33 and the cylinder 32 between a loading positionand an injecting position.

[0034] As will be understood from the foregoing description, the moldingapparatus has three movable components, i.e., the lower half 24, theplunger 34 and the base plate 33, and changes the relative positions ofthe movable components 24, 34 and 33 during a packaging operation asdescribed hereinlater. The relative positions shown in FIG. 3A arereferred to as an initial position. The heater HE, the electric powersource PW, ejector pins 29, the knock out plates 30, the drivingmechanism 31, the base plate 33, the knock out rods 41, thehydro-pressurizing system 35 and the lifter 42 are deleted from FIGS. 3Bto 3F for the sake of simplicity.

[0035]FIGS. 4A to 4E illustrates a process for packaging a semiconductorchip in synthetic resin embodying the present invention, and FIG. 5illustrates the relative positions between the three movable components,i.e., the lower half 34, the base plate 33 and the plunger 34.

[0036] Firstly, the molding apparatus keeps the three movable components24, 33/32 and 34 in the initial position shown in FIG. 3. The lower half34 is spaced from the upper half 23, and the base plate/cylinder 33/32and the plunger 34 are in the loading position and the lower limit,respectively. Granular synthetic resin 43 is loaded into the pot 27, andsemiconductor bare chips 44 mounted on a lead frame 45 is placed on thelower half 24 as shown in FIG. 4A.

[0037] The electric power source PW supplies electric current to theheater HE at time t1, and the heater HE starts to melt the granularsynthetic resin 43 in the pot 27. The driving mechanism 31 starts tomove the lower half 24 toward the upper half 23 at time t2, and thelower half 24 is brought into contact with the upper half 23 at time t3.Then, the molding die 21 enters into the closed position.

[0038] The heater HE heats the granular synthetic resin 43 until timet4, and makes the granular synthetic resin 43 softened as shown in FIG.4B. In this instance, time interval T between time t2 and t4 is equal toor less than 25 seconds, and the granular synthetic resin 46 becomessoft available for injection. The lifter 42 and the hydro-pressurizingsystem 35 start to upwardly move the base plate/cylinder 33/32 and theplunger 34 at time t4. The plunger 34 pushes the soft synthetic resin 46toward the upper half 23, and the soft synthetic resin 46 is pressedagainst the upper half 23 as shown in FIG. 4C. As a result, the airmixed into the granular synthetic resin 43 is evacuated from the softsynthetic resin 46.

[0039] The plunger 34 continuously applies pressure to the softsynthetic resin 46, and pushes out the soft synthetic resin 46 into therunner 28 as shown in FIG. 4D. The plunger 34 reaches the upper limit attime t5, and the soft synthetic resin 46 is spread over the cavities25/26 as shown in FIG. 4E. Thus, the semiconductor bare chips 44 mountedon the lead frame 45 are sealed in a synthetic resin package.

[0040] Subsequently, the driving mechanism 31 starts to downwardly movethe lower half at time t6, and the plunger is retracted into thecylinder 32. The lifter 42 starts to downwardly move the cylinder 34 andthe base plate 33 at time t6, and stops the cylinder 34 and the baseplate 33 at an intermediate position at time t7. The plunger 34 isseparated from the synthetic resin package. The lower half 34 reachesthe lower limit at time t8, and the molding die 21 enters into the openposition.

[0041] The lifter 42 starts to upwardly move the base plate 33 and thecylinder 32 at time t8, and the knock out rods 41 are brought intocontact with the knock out plates 30 on the way toward the injectingposition. The plunger 34 is lifted together with the cylinder 32, andthe plunger 34 is brought into contact with the synthetic resin packagealso on the way toward the injecting position. The base plate/cylinder33/32 and the plunger 34 are further moved upwardly by 1-2 millimeters,and separate the synthetic resin package from the lower half 24 at timet9. Thus, the synthetic resin package is separated from the lower half24, and is taken out from the molding die 21 until time t10.

[0042] The lifter 42 starts to downwardly move the base plate/cylinder33/32 at time t10, and the molding apparatus returns to the initialposition at time t11.

[0043] As will be appreciated from the foregoing description, theplunger 34 presses the soft synthetic resin 46 against the upper half 23so as to evacuate the air therefrom. For this reason, a void does nottake place in the synthetic resin package. The soft synthetic resin 46is directly produced from the granular synthetic resin 43, and theprocess is simple. Moreover, the soft synthetic resin 46 is pressed inthe molding die 21, and the molding apparatus is simple.

Second Embodiment

[0044]FIG. 6 illustrates another process for packaging a semiconductorbare chip in synthetic resin embodying the present invention. Themolding apparatus shown in FIG. 3 is used in the process implementingthe second embodiment. The second embodiment is only different from thefirst embodiment in the motion of the plunger 34, and the lower half 34and the base plate/cylinder 33/32 behave as similar to those of thefirst embodiment. For this reason, description is focused on the plunger34.

[0045] The granular synthetic resin 43 is also heated from time t2 totime t4, and the time interval T is equal to or less than 25 seconds. Inthis instance, when the lower half 24 is brought into contact with theupper half 23, the hydro-pressurizing system 35 starts to upwardly movethe plunger 34. If the pot 27 is small in diameter, only a small amountof granular synthetic resin 43 is supplied to the pot 27, and thegranular synthetic resin 43 is immediately softened. For this reason,the plunger 34 is moved at the entry into the closed position, andevacuates the air from the soft synthetic resin 46 by applying pressurethereto. When the pot 27 has the diameter equal to or less than 15millimeters, the second embodiment is desirable.

[0046] The second embodiment achieves all the advantages of the firstembodiment, and enhances the throughput.

Third Embodiment

[0047]FIG. 7 illustrates yet another process for packaging asemiconductor bare chip in synthetic resin embodying the presentinvention. The molding apparatus shown in FIG. 3 is used for thepackaging process implementing the third embodiment. The relativepositions from time t7 to time t12 is similar to the relative positionsfrom time t6 to time t11 of the first embodiment, and description isfocused on the relative positions from time t1 to time t6.

[0048] The heater HE starts to heat the granular synthetic resin at timet1, and the granular synthetic resin 43 is softened. The drivingmechanism 31 starts to upwardly move the lower half 34 at time t2. Thehydro-pressurizing system 35 upwardly moves the plunger 34 at time t3,and applies pressure to the soft synthetic resin 46 so as to eliminatethe air from the soft synthetic resin 46. The lifter 42 starts toupwardly move the base plate/cylinder 33/32 at time t3, and the baseplate/cylinder 33/32 reaches an intermediate position on the way to theupper limit at time t4. The lower half 34 is brought into contact withthe upper half 33 at time t4. When the base plate/cylinder 33/32 reachesthe intermediate position, the plunger 34 pushes out the soft syntheticresin 46 into the runners 28, and the soft synthetic resin 46 proceedsto the boundary between the runners 28 and the cavities 25/26 as shownin FIG. 4D.

[0049] The heater HE stops heating at time t5, and the time period Tbetween time t1 and time t5 is 25 seconds. The lifter 42 starts tofurther upwardly move the base plate/cylinder 33/32 at time t5, andreaches the upper limit at time t6. While the base plate/cylinder 33/32are being upwardly moved together with the plunger 34, the softsynthetic resin 46 flows into the cavities 25/26, and the semiconductorbare chaps 44 are sealed in the synthetic resin 46.

[0050] The synthetic resin 46 is heated until time t5, and the softsynthetic resin 46 is never solidified in the runners 28. For thisreason, the packaging process is desirable for the molding die 21 withthe longest runner 28 greater than 30 millimeters. The heater HE startsto soften the granular synthetic resin 43 before the upward motion ofthe lower half 34, and accelerates the molding operation.

Fourth Embodiment

[0051]FIGS. 8A and 8B illustrate essential steps of still anotherprocess for packaging a semiconductor bare chip in synthetic resinembodying the present invention. A molding apparatus used for the fourthembodiment is different from the molding apparatus shown in FIG. 3. Athrough-hole 23 a is formed in the upper half 23, and is located overthe pot 27. A plunger 50 is slidably inserted into the through-hole 23 aas shown in FIG. 8A, and is projectable into the pot 27. The cylinder 32is not provided for the plunger 34, and the soft synthetic resin 46 ispressed by the plunger 32 instead of the plunger 34 as shown in FIG. 8B.The plunger 50 applies pressure to the soft synthetic resin 46 for 0.5second, and returns to the initial position shown in FIG. 8A.

[0052] The process implementing the fourth embodiment is similar to thefirst embodiment except for the pressurization by using the plunger 50.The step shown in FIG. 8A and the step shown in FIG. 8B arecorresponding to the step shown in FIG. 4B and the step shown in FIG.4C. The other steps are similar to those of the first embodiment, and nofurther description is incorporated hereinbelow for the sake ofsimplicity.

[0053] As will be appreciated from the foregoing description, the softsynthetic resin is pressed before the injection, and the pressurizationeliminates the air mixed in the granular synthetic resin from the softsynthetic resin. For this reason, the soft synthetic resin is directlyproduced from the granular synthetic resin, and the process sequenceand, accordingly, the molding apparatus are made simple.

[0054] Although particular embodiments of the present invention havebeen shown and described, it will be obvious to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the present invention.

[0055] For example, the plunger 50 may be controlled as similar to theplunger 34 in the process implementing the second embodiment. Namely,when the lower half 24 is brought into contact with the upper half 23,the plunger 50 is downwardly moved so as to press the soft syntheticresin 46 for 0.5 second. Then, the plunger 50 returns to the initialposition, and, thereafter, the plunger injects the soft synthetic resin46 into the cavities 25/26.

[0056] Vacuum may be created in the cavities 25/26 from the entry intothe closed position to the completion of the injection. The vacuumenhances the injection efficiency, and perfectly eliminates void fromthe synthetic resin package.

[0057] The packaging processes according to the present invention areavailable for any kind of product to be sealed in a synthetic resinpackage.

What is claimed is:
 1. A process for packaging a product in syntheticresin, comprising the steps of: a) accommodating a product and granularsynthetic resin in a molding die; b) softening said granular syntheticresin so as to produce soft synthetic resin; c) applying pressure tosaid soft synthetic resin so as to evacuate the air therefrom; and d)spreading said soft synthetic resin over an inside space of said moldingdie so as to seal said product in a synthetic resin package.
 2. Theprocess as set forth in claim 1 , in which said product is asemiconductor bare chip mounted on a lead frame.
 3. The process as setforth in claim 2 , in which heat is applied to said granular syntheticresin for 25 seconds or less so as to soften said granular syntheticresin.
 4. The process as set forth in claim 2 , in which said step c)starts immediately after completion of said step b).
 5. The process asset forth in claim 2 , in which said step c) starts before completion ofsaid step b).
 6. The process as set forth in claim 5 , in which saidsoft synthetic resin is supplied from a pot to said inner space, andsaid pot has a diameter equal to or less than 15 millimeters.
 7. Theprocess as set forth in claim 5 , in which said step d) startsimmediately after completion of said step b).
 8. The process as setforth in claim 5 , in which said step d) starts before completion ofsaid step b).
 9. The process as set forth in claim 8 , in which saidinner space has cavities for accommodating said product and runnersguiding said soft synthetic resin to said cavities, and said step d)includes the sub-steps of d-1) introducing said soft synthetic resininto said runners before said completion of said step b), d-2)introducing said soft synthetic resin into said cavities after saidcompletion of said step b).
 10. The process as set forth in claim 9 , inwhich at least one of said runners has a length greater than 30millimeters.
 11. A molding apparatus comprising a molding die formedwith cavities for accommodating a product and runners connected to saidcavities, a pot connected to said runners and accommodating granularsynthetic resin, a heating means associated with said pot for heatingsaid granular synthetic resin so as to produce soft synthetic resin, apressurizing means associated with said pot and applying pressure tosaid soft synthetic resin so as to evacuate the air therefrom, and aninjecting means associated with said pot and injecting said softsynthetic resin through said runners into said cavities after theevacuation of said air.
 12. The molding apparatus as set forth in claim11 , in which a plunger projectable into said pot is shared between saidpressuring means and said injecting means.
 13. The molding apparatus asset forth in claim 11 , in which said pressurizing means has a firstplunger projectable into said plot in a first direction, and saidinjecting means has a second plunger projectable into said plot in asecond direction different from said first direction.